There are three commonly used press release formats.  Each one has a different purpose.

Format #1:  the news release.  This is perhaps the most common press release format, and it's also the most misused.  From its namesake, the news release is supposed written for journalists (not the end user) and cover a newsworthy topic about the company, product or service.  It's not meant to be a promotional write-up.  Unfortunately, many news releases that are sent to journalists do not have any news angle in their content (or the news is buried in the last paragraphs of the release).  Since a can scan mounds of releases every week or even every day for an interesting news items to include in stories, bad releases are generally immediately trashed. 

Format #2: the tip sheet. This press release format provides a list of advice tips on a focused topic. It's general style includes an eye-grabbing headline, an introductory paragraph that gives some background of the issue at hand, and then the list of bulleted points.  Sometimes tip sheets are distributed like news releases (to journalists), or they are included in a company's press kit.

Some examples of a tip sheet might include:

"14 ways to save water in dry climates"
"6 ways to get more mileage on your car"

Format #3: the media alert.   A media alert is more of a memo-styled press release format and is used to make an announcement to the media about an upcoming event.  For example, if you were a guru on a certain topic and were going to be speaking at an important related conference, you might send a media alert to TV and radio stations in hopes that they would come an cover the event and interview you.